1. Field of the Invention
This invention relates to a two-temperature pneumatic thermostat control system as well as to a two-temperature pneumatic thermostat control unit for such a system or the like.
2. Description of the Prior Art
It is known to provide a two-temperature pneumatic thermostat control system having an output device, a two level source of pneumatic pressure, a first temperature sensor for controlling the flow of pneumatic fluid from the source to the device when the source is at a first level thereof, a second temperature sensor for controlling the flow of pneumatic fluid from the source to the device when the source is at a second level thereof, a switching means for automatically switching the device to be controlled by the first sensor when the source is at the first level thereof and by the second sensor when the source is at a second level thereof, and manual reset means for causing the switching means to switch the device to be controlled by the first sensor even though the source is at the second level thereof when the reset means is moved to a reset position thereof.
For example, see the following item:
(1) See the control system and unit labeled as prior art in FIG. 1 of this application.
It can be seen that the reset lever of the system and unit of item (1) above operates a single valve member which can either move to an open or a closed position so that an orifice is required in the system to prevent a dumping of the source vacuum when the reset lever is utilized to move the valve member to a vent position thereof.